1. Field of the Invention
The present invention relates to an active control system of the type including a fluid-operated piston-cylinder unit for moving a movable member, wherein provision is made for opening a fluid connection to the unit in emergency conditions to permit axial displacement of the piston rod relative to the cylinder.
2. The Prior Art
FIG. 7 of DE 42 24 132 discloses an active door-locking system that has a piston-cylinder unit which is connected by connecting lines to a pump unit. An on-off valve permits regulation of the flow of pressure medium into a working chamber of the piston-cylinder unit. Such a system allows a door or tailgate motion in a motor vehicle, for example, to be performed very conveniently by operation of the piston-cylinder unit.
In the case of such active control systems, it should be considered that fingers or objects may possibly be pinched when, for example, a vehicle is being loaded. Physical harm to humans or damage to the goods loaded would be the unfortunate consequence.
In addition, the supply of energy may be interrupted, so that the control system is no longer capable of performing the control motion automatically. In such circumstances, the possibility that the door or tailgate cannot be opened must be avoided, because otherwise one could be trapped in the vehicle.